Insights into Arctic Cyclones and Tropopause Polar Vortices from Data Assimilation in Variable Resolution CESM2

The evolution of Arctic cyclones is governed by processes from the surface through to the tropopause. At the tropopause, long-lived, sub-synoptic features known as tropopause polar vortices (TPVs) are frequent precursors to the development of Arctic cyclones. At the surface, baroclinicity is important for the initiation and intensification of Arctic cyclones. The sea ice state also influences the development of Arctic cyclones, while itself experiencing rapid changes as a result of these cyclones. The evolution of Arctic cyclones and TPVs is also sensitive to the profile of radiant heating throughout the troposphere, on which the vertical distribution of water vapor is an important control. Accurate representation of Arctic cyclones in weather and climate models requires that each of these processes be represented.

We use the Community Earth System Model 2 (CESM2), combined with the Data Assimilation Research Testbed (DART), to perform a hierarchy of observing system simulation experiments designed to isolate important processes in Arctic cyclone and TPV development for a case in August 2016. We use both atmosphere-only and coupled sea ice-ocean-atmosphere configurations to analyze the influence of surface coupling. A configuration of the CAM-SE atmosphere with enhanced spatial resolution over the Arctic is used to achieve the resolution necessary to resolve sub-synoptic TPVs, while avoiding the excessive computational costs of a global high-resolution model. Early results highlight the importance of accurately representing the vertical distribution of water vapor and its influence on AC and TPV coupling and intensification, and highlight the sensitivity of Arctic cyclone intensification to their position relative to TPVs.